Hering, L., Henze, M. J., Kohler, M., Kelber, A., Bleidorn, C., Leschke, M., et al. (2012). Opsins in onychophora (velvet worms) suggest a single origin and subsequent diversification of visual pigments in arthropods. Molecular Biology and Evolution, 29(11), 3451-3458. doi:10.1093/molbev/mss148.